1. Field of the Invention
The present invention relates to a device that can evaluate the soundness of a valve device and to a system that can judge whether the valve device is opened or closed.
2. Description of the Related Art
Conventionally, there is a method by which strain and torque are measured by a strain gauge attached in the vicinity of a valve driver so as to monitor the soundness of a valve drive unit and to estimate the degree of abnormality and deterioration based on the change over time. For example, as described in JP-A-8-261355, a strain gauge is mounted onto an immovable hollow circular cylinder disposed in the vicinity of the valve stem to measure torque and thrust.
In the above-mentioned patent document, there is a problem in that because a strain gauge that is a conventional strain measurement device is used, when the temperature in the valve device changes, sensitivity of the gauge cannot be sufficiently compensated and small changes of thrust and torque cannot be measured. For example, when measuring frictional force or torque at the time a valve opens or closes, highly accurate measurement is necessary; however, there is a problem in that if the temperature of the piping to which the valve is installed changes, sufficiently accurate measurement is not possible.
Furthermore, there is a problem in that motors or relays which become a major noise source are often disposed in the vicinity of the location where a strain measurement device is attached, thereby making accurate measurement impossible because the strain gauge tends to pick up that noise. Specifically, when conducting remote monitoring, there is a problem in that if a resistance value of the strain gauge increases so as to reduce current consumed by a measurement system, data on small strain is greatly interfered by noise, thereby decreasing the measurement accuracy.
Furthermore, because a plurality of strain gauges, which are conventional strain measurement devices, are usually required to be attached, there is a problem in that a large enough area is required, then it is difficult to attach those strain gauges to a small valve device, and maintenance inspection may be interfered. Specifically, there is a problem in that a wireless system which conducts remote monitoring requires a large device, which tends to hinder the maintenance inspection of the valve device from being easily conducted.
Furthermore, as described in JP-A-8-261355, when measuring torque and thrust by using a strain gauge, it is necessary to attach a plurality of strain gauges so that they are orthogonal to each other and have a specific angle to the valve stem. However, from the practical point of view, it is difficult to attach the gauges to a complicated shaped component such that they are orthogonal to each other, and an error of the angle at which gauges were installed tends to be generated. That is, there is a problem in that accurate measurement is impossible due to an error of the angle at which gauges were installed.
Furthermore, there is a problem in that because thin film which functions as a strain detection portion of a strain gauge has a fatigue life, it is not reliable enough to be used for a long period of time required during the life time of a valve device.
Furthermore, because the measurement system of a valve device remotely monitors the valve device's abnormality and evaluates its life, the measurement system is often driven by a battery, low electric power, or an RF power supply. However, in that case, there is a problem in that power consumption of the strain gauge must become large to prevent noise; accordingly, electric power is insufficient resulting in limited operation time.
Moreover, conventionally, strain generated at the time a strain gauge is attached cannot be compensated. For this reason, there is a problem in that if gain of a strain gauge is increased at the time of wireless transmission so as to conduct accurate measurement, the value exceeds the measurement range.